1. Field of the Invention
The present invention relates to a printing plate sucker which simultaneously suction-adheres both of a printing plate and a protective sheet, which is superposed on an upper face of the printing plate, from the protective sheet side thereof and sheet-feeds the same.
2. Description of the Related Art
Technology (printing plate exposure devices) has been developed which, using a printing plate at which a recording layer (photosensitive layer) is provided on a support (for example, a PS plate, a thermal plate, a photopolymer plate or the like), records an image at the photosensitive layer (an image formation surface) of this printing plate with a direct laser beam or the like. With such technology, rapid image recording on printing plates is enabled.
Now, in a printing plate automatic exposure device which uses this technology for image recording onto printing plates, a large number of printing plates are stacked and accommodated in a cassette. The image-recording formation surfaces of the printing plates are easily damaged. In order to protect these image formation surfaces, protective sheets (interleaf sheets) are superposed with the image formation surfaces of the printing plates. These are stacked in successive layers and accommodated in the cassette. At a time of sheet-feeding the printing plates, one end portion of a topmost printing plate of the plurality of printing plates that are stacked in the cassette is suction-adhered by a sucker and separated from the other printing plates. Thus, the printing plates are taken out one by one and sheet-fed (conveyed and supplied) to a subsequent process (for example, an exposure process) while being inverted (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-247489).
Anyway, when printing plates are suction-adhered to be taken out one at a time and sheet-fed while being inverted as described above, besides a force on the sucker in a perpendicular direction (a load from the printing plate), a moment caused by this load acts on the sucker at a sucker suction position (a lifting position). In the case of a conventional, ordinary rubber sucker, the whole of the sucker is a resilient body of rubber or the like. Therefore, when this moment acts, the sucker itself (a skirt portion thereof) deforms in accordance with the moment, and the printing plate inclines with respect to an axial direction (the perpendicular direction) of the sucker (i.e., a position of loading effect is displaced with respect to the sucker). As a result, a state in which the moment is reduced is attained. Thus, the moment acts such that a practical limit of suction capability is increased, and suction-adherence and sheet-feeding of the printing plates is not hindered (ordinarily, a perpendicular component of a suction force of the sucker is stronger than the moment).
However, for this kind of printing plate automatic exposure device, in recent years, providing the protective sheets with slight permeability to air has been considered (see, for example, Japanese Patent Application No. 2001-378460 submitted by the present applicant). Hence, both the printing plate and the protective sheet, which is superposed with the printing plate, are simultaneously suction-adhered and sheet-fed as a pair, using the sucker from the protective sheet side thereof. The purpose of this is to shorten a sheet-feeding cycle time, simplify a sheet-feeding structure, reduce space requirements of the sheet-feeding structure, and to lower costs and the like.
In the case of a conventional, ordinary rubber sucker, when the sucker itself is deformed by the moment that acts during the suction-adherence and sheet-feeding as described above, there is a possibility that the protective sheet superposed with the printing plate will be hoistingly deformed, and wrinkling may occur. When wrinkling is caused in this manner at the protective sheet during suction by the rubber sucker, an air leak is formed between the protective sheet and the printing plate, and it becomes impossible to suction-adhere and sheet-feed the printing plate and the protective sheet together at the same time.